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--- ----------------------------------------------------------------------------
--- This module provides some utility functions for function application.
---
--- @author Bjoern Peemoeller
--- @version July 2013
--- @category general
--- ----------------------------------------------------------------------------
module Data.Function (fix, on) where

--- `fix f` is the least fixed point of the function `f`,
--- i.e. the least defined `x` such that `f x = x`.
fix :: (a -> a) -> a
fix f = let x = f x in x

--- `(*) \`on\` f = \\x y -> f x * f y`.
--- Typical usage: `sortBy (compare \`on\` fst)`.
on :: (b -> b -> c) -> (a -> b) -> a -> a -> c
on op f x y = f x `op` f y